In many applications, the tightening of threaded fasteners to a specific degree or torque is of extreme importance. For example, in the assembly and maintenance of aircraft, every bolt, screw, and nut has a prescribed torque value and limit set by the American Society of Mechanical Engineers that is required for the aircraft to operate properly. Undertightening results in the fastener not working properly while overtightening may strip the threads of the fastener, break the fastener off in a threaded hole, or create vibrational problems in the resulting assembly.
Traditionally, torque wrenches have been used for tightening these devices. In addition to tightening the fastener, a torque wrench provides the user with an indication of the exact torque being applied. Some torque wrenches include indicators that provide a visual indication of the torque being applied so that the operator does not apply a greater torque than intended. A straight forward example is the bendable beam-type wrench with a strain gauge marked with numbered graduations. In this example, torque is indicated by the degree of deflection of the bendable beam relative to the strain gauge. Visually indicating torque wrenches are not useful in applications where visual observation of the torque indicator is obstructed or otherwise made difficult.
To overcome this problem, torque wrenches that provide a non-visual indication when a predetermined torque has been reached, such as an audible “click” or a movement providing “feel” to the operator, have been developed. These wrenches utilize spring tension to determine the amount of torque applied to tighten a threaded fastener and employ a mechanism that uses some type of metallic member that is released when the desired torque is obtained, thus striking the housing or other part of the wrench to produce an audible clicking sound.
The most popular type of this wrench is called a micrometer torque wrench and has a hollow arm which includes a spring and pawl mechanism for setting the torque. Within the hollow arm, the pawl is forced against one end of a bar that is connected to a drive head, the bar and a drive head are pinned to the hollow arm and rotate as torque is applied. The pawl is released when the force applied by the bar increases beyond a set value established by the operator. When released, the bar hits the inside of the arm, producing a sound and a distinct feel by a user. The torque value or release point is changed by rotating the handle, which moves on threads for setting. Additionally, values are permanently stamped or imprinted on a scale that is located on an outer surface of the hollow arm. Micrometer wrenches can overtorque when the operator continues to apply pressure after release, due to the momentum created by the releasing mechanism. This overtorque may occur without the user even realizing it. To solve this problem, “cam-over” wrenches replace the pawl with a ball bearing or roller held within a detent. A spring holds the ball within the detent and when the torque on the drive overcomes the spring force on the ball, the ball displaces and the ratchet rotates.
Adjustable torque wrenches have handles that can be turned to vary the compression of a spring, which, when properly calibrated, corresponds to a certain torque value. Traditionally, a user has to turn the handle inward to compress the spring and set the wrench for higher torque values. At higher torque settings, this tool requires users to strain to turn the handle as it compresses against the main body of the tool. Also, this inward turning shortens the length of the tool. Again, more user-applied force is required to use a shorter tool when a higher torsional force is needed. The increased demand on the user decreases the amount of control the user has on the tool, which may result in injury to the user. The decreased control also exacerbates the common problem of the tool head slipping off of the work-piece, which can result in damage to the work-piece, the tool, or the operator.
On Aug. 28, 1984, U.S. utility Pat. No. 4,467,678 (filed Aug. 27, 1982) was granted to Lindholm. The title of the publication is “Torque Wrench.” The content of this publication is incorporated by reference into this patent application as if fully set forth herein.
On Dec. 4, 1984, U.S. utility Pat. No. 4,485,703 (filed May 20, 1983) was granted to Grabovac. The title of the publication is “Torque Wrench.” The content of this publication is incorporated by reference into this patent application as if fully set forth herein.
On Jul. 17, 1980, U.S. utility Pat. No. 4,207,783 (filed Apr. 14, 1978) was (granted to Grabovac. The title of the publication is “Torque Wrench.” The content of this publication is incorporated by reference into this patent application as if fully set forth herein.
On Nov. 20, 1973, U.S. utility Pat. No. 3,772,942 (filed Jul. 27, 1972) was granted to Grabovac. The title of the publication is “Adjustable Torque Wrench.” The content of this publication is incorporated by reference into this patent application as if fully set forth herein.